The Animal Core (Core B) is responsible for providing experimental animals for Projects by Ison, Walton and Frisina of the Program Project. The primary responsibility is to breed and maintain specific pathogen free mice (Mus musculus) and gerbils (Meriones ungulatus) in a acoustically controlled, low-noise environment, so that they can be used at various ages in behavioral, neurophysiological, and anatomical experiments carried out by Projects by Ison, Walton and Frisina. The Animal Core will maintain various rodent colonies for experimentation, including CBA/CAJ and C57Bl/6J inbred mice, F1 hybrids of these two strains, two potassium channel (Kv1.1, Kv1.2)"knockout" mouse strains, and outbred gerbils. Besides rearing and maintaining rodents, the animal core also has other major responsibilities in the service of Projects by Ison, Walton, and Frisina. These include 1) tagging all subjects for identification; 2) maintaining life- and experimental history databases on all subjects; 3) performing diagnostic auditory brainstem response evoked potential measurements to ascertain audiometric thresholds on all animals before and during experiments; 4) transporting subjects to the laboratories and scheduling cross-project experiments on individual subjects; and 5) obtaining tissue samples for genotyping of potassium channel "knockout" mice. Thus, the Animal Core provides essential centralized services to all Program Project laboratories working with rodents.